Actual Dyno tests indicate 3.9 HP with a stock head. The power increases to 4.65 HP with a re-worked and milled head. Adding an aftermarket head, and 26 MM carburetor pushes it into the high 5 HP range.

Hi Smitty,
I have tried many different camshafts and ended up with as many different results. I have worked closely with a camshaft company located in NC and have produced motors that can exceed 8000 RPMs acheive 40.3 MPH in 150 Feet.
However the best camshaft for over all performance is the NE camshaft [early is best, but scarce]. Always remember the higher lift camshafts must use mushroom lifters.

The WC-1 camshaft and a set of mushroom lifters produce the most low to midrange power on the new edition Whizzers. Using the WC-1 camshaft on an NE motor with the larger 24 MM intake valve, mushroom lifters, and a correctly jetted carburetor will make more power below 3000 RPMs than the NE camshaft. Good news! I and I am sure many Whizzer dealers have WC-1 camshafts in stock. I sold a bunch of them last year to a company that was after the gears to put on billet camshafts. BTW they list for $82.85, but I sold them for $35.00 each as a used part. If you want to try one, let me know.

I know what you are looking for, because I raced a lot of "thumpers" on the dirt track and often on small tight tracks, bottom end power was required to win. I raced BSA 500 singles, Ducati 250/350/450 singles, and even the HD 250 single [4 stroke made in italy]

Send me the cam with your invoice, and I'll mail you my check, just like I did for the Mushroom Lifters.

Two More questions:

For a cam grind to favor the low RPM segment of an engine's RPM range, it must use a profile with little or no overlap, allowing intake and exhaust valves to stay open only for their 180 degrees of crankshaft rotation.

Am I right?

(No, I was never employed as Ed Iskenderian's Chief Design Engineer.):grin5:

ALso, would I really be able to feel a slight boost in low-end torque?

Some confusion can arise surrounding the different things related to the term "needle" in slide type carburetors.

Needle Valve - a valve activated by the carb float that shuts off fuel to the bowl

Jet Needle - the long tapered needle, mounted in the carb slide, that moves in and out of the "needle jet" as throttle position is varied, and controls the fuel mixture from just off idle to about 7/8 throttle. The top of the "jet needle" has a series of grooves cut into it at different heights to allow it to be positioned at different heights in the slide, which in turn position it at different heights in the "needle jet", ultimately altering the fuel/air mixture.

Needle Jet - the jet that is centered below the slide and in which the "jet needle" resides. The "jet needle" moves in and out of the "needle jet" as the slide is moved.

This would mean that the throttle would have to be opened a little wider before the needle lifts out if the needle valve, according to my understanding of the slide-type throttle cutaway sketch. Am I seeing this right?

Now what about the "Main Jet", the one most frequently changed...where is that?

Hi Hal
The needle actually controls the flow of fuel through the main jet. If you have a large main jet, you will have more fuel from just off idle to wide open throttle. By moving the clip on the needle up or down you are using the taper of the needle to meter the fuel at almost all throttle positions. Raising the clip on the needle lowers the needle and makes the mixture leaner. Lowering the clip raises the needle and makes the mixture richer. The size of the main jet determines how much fuel the needle has to work with. Hope this helps.

Jim

P.S. The main jet in located in the carb float bowl. It is in the center right where the needle will slide in and out. It is brass with a slot across the face with a small hole in the center.

You are seeing it correctly, and lowering the needle will lean the entire range over which the needle jet is operable.

Regarding the main jet, look at the exploded view in the 1st link I sent and find item #36 near the bottom the illustration - this is the main jet. Depending on the particular carb model, the main jet may be mounted vertically in the bottom of the carb stem, or may be mounted horizontally near the bottom of the carb stem. Regardless of which of these positions it is in, the main jet function is identical, i.e., it supplies fuel to the needle jet circuit at partial throttle positions, and is the sole metering device at wide open throttle (WOT). If you view the second link above you can see which circuits are recruited and blended at the various throttle positions.

All fuel fed through the needle jet/jet needle circuit must 1st pass through the main jet, as this is the only fuel supply for the needle jet. The main jet can obviously pass more fuel than is required by the needle circuit, thus it is not metering anything until you are nearly at WOT. At WOT the jet needle is essentially withdrawn from the needle jet and the circumferential area between the jet needle and needle jet becomes so large that the needle circuit becomes inactive, leaving the main jet is the sole metering device.

To provide an example of main jet size influencing needle circuit operation consider the following. A friend of mine was attempting to size a main jet correctly for an experimental engine, running a smooth bore Mikuni, and installed a series of increasingly larger main jets in his side valve engine and test drove it after every change to determine when it was too rich. The jet size varied from a quite small (which was about the correct size) to quite large (dia increased 1.4x over starting point, which is a huge change, and would make any engine pig rich). He could tell no difference at all between any of the jet sizes, finding that the bike ran equally well with all of them. Well, we knew this couldn't be true, yet it actually happened. So what was actually going on here? Well, come to find out after the fact, he looked in his carb one day and found that, due to incorrect twist grip travel, he was only opening the slide about 3/4 of the way, so in fact he never was on the main jet, only the needle circuit. In this case even though the main jet was huge it did not significantly alter the operation of the needle circuit. If he ever would have opened it up with the huge main jet present, it would have fallen flat on it's face, blubbering and stuttering to a standstill.